Convert binary data to base64 with javascript

To prevent 'InvalidCharacterError' error, you need to do this:

var base64EncodedStr = btoa(unescape(encodeURIComponent(rawData)));

Use a FileReader to encode your image as a data URL:

jQuery.ajax({...})
.done(function (r) {
  var reader = new FileReader(
  reader.onload = (function(self) {
    return function(e) {
      document.getElementById("img").src = e.target.result;
    }
  })(this);
  reader.readAsDataURL(new Blob([r]));
});